Physical security continues to become increasing important in today's world. The ability of a sensor to detect an intruder passing through that sensor's detection envelope with high probability of detection (POD) and minimum nuisance alarm rate (NAR) is of the utmost importance. Up to now, active infrared (AIR) sensors have been used to create active beams that when broken, indicate an intrusion. AIR sensors have inherent physical limitations such as generation of high nuisance alarms when subjected to low sun angles, rain, snow, fog, high ground temperatures, and dust. For example, at low sun angles, AIR sensors may be in constant alarm or result in spurious behavior because sunlight contains sufficient intensity and IR content that interferes with the AIR sensor. The security industry has not invested much effort to modify the fundamental AIR designs to reduce NAR and improve low performance from low sun angles.
What is needed are intrusion detection systems and methods that are less prone to NAR sources, such as rain, snow, fog, high temperatures, and dust, and will function reliably when the sensor is subjected to low sun angles.
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